Brittny Gastineau was bounced from backstage at a Backstreet Boys concert in Vegas at the request of her ex-boyfriend Nick Carter‘s new love, Lauren Kitt. A spy said Kitt, who has a striking resemblance to Brittny, asked fellow boy-bander Howie Dorough to have security ask Gastineau and her mom, Lisa, to leave. Gastineau walked out without a fight Sunday, but her friend told us, “She was shocked by the diss. She hasn’t been with Nick in five years.” The friend said Brittny, daughter of ex-Jet Mark Gastineau, is dating actor-producer Eli Roth, newly liberated from Peaches Geldof. Gastineau declined to comment, and Carter’s rep didn’t get back to us.